1. Field of the Invention
The present invention relates to a surfactant composition. More specifically, it relates to a surfactant composition in which the rinsing properties of a sulfonic acid salt of a lower alkyl ester of a saturated fatty acid are improved.
2. Description of the Prior Art
Sulfonic acid salts of lower alkyl esters of saturated fatty acids, i.e., alpha-sulfo fatty acid ester salts, are surfactants having excellent detergency (i.e., detergent power) and hard-water resistance. However, alpha-sulfo fatty acid ester salts have disadvantages in that vigorous foaming occurs at a low concentration and, therefore, the rinsing properties are poor when they are incorporated into household detergents such as laundry detergents and dish-washing detergents, when compared with other conventional surfactants such as alpha-olefin sulfonates, alkylbenzene sulfonates, or sulfates of higher alcohols.
As an improvement for the above-mentioned rinsing properties of alpha-sulfo fatty acid ester salts, Japanese Unexamined Patent Publication (Kokai) No. 53-97008 discloses the use of alpha-olefin sulfonates and sulfuric acid ester salts of alcohols combined with alpha-sulfo fatty acid ester salts. However, the rinsing properties of alpha-sulfo fatty acid ester salts were not satisfactorily improved as desired. Thus, it remains necessary that the above-mentioned disadvantages and problems of alpha-sulfo fatty acid ester salts should be fundamentally resolved.
It is known that the rinsing properties, that is, the foaming at a low concentration of the surfactant are closely correlated to a critical micelle concentration (CMC) of the surfactants. When the CMC is low, a large amount of foam is likely to be formed at a low surfactant concentration and the rinsing properties become poor. Conversely, the foaming becomes less at a low surfactant concentration and, therefore, the rinsing properties are improved, as the CMC increases. It is expected that the increase in the CMC of the surfactants can be achieved by decreasing the hydrophobic nature of a hydrophobic group of the surfactant molecule or by increasing the hydrophilic nature of a hydrophilic group. However, when the hydrophobic nature of a hydrophobic group of the surfactant molecule is decreased or the hydrophilic nature of a hydrophilic group of the surfactant molecule is increased, the characteristics of the surfactants affecting the detergency of the surfactants such as foaming power, penetrating power, and solubilizing power, are decreased. Accordingly, there is a need in the art for increasing the CMC of the surfactants, and improving the rinsing properties of the surfactants, without decreasing the characteristics required of detergents.